A snapshot copy of a production file system contains the state of the production file system at a respective point in time when the snapshot copy is created. A snapshot copy facility can create a snapshot copy without any substantial disruption to concurrent read-write access to the production file system. Such a snapshot copy facility, for example, is described in Keedem U.S. Pat. No. 6,076,148 issued Jun. 13, 2000, incorporated herein by reference. Snapshot copies have been used for a variety of data processing and storage management functions such as storage backup, transaction processing, and software debugging.
Users are becoming less tolerant of delays in accessing their data, and even less tolerant of corruption of their data. Therefore, there has been a continuing interest in improving data availability and the effectiveness of recovery procedures. For example, after recovery, the integrity of the recovered file system is checked, and if a defect is found, an attempt is made to correct it. In addition, it is often possible to recover some of the data that was written to the production file system since the creation of the latest read-only version, for example, by replay of a log from an application program.